Developed for Prairie Horizons Farm with OnFarm Storage Inc. and the University of Minnesota, the Produce Hydrocooler is a small scale system designed to quickly cool organic produce through forced convection. The system is designed to interface with an existing milk chiller for its cold water supply and has a storage capacity in excess of Prairie Horizon's predicted peak harvest. Water is pumped from the milk chiller to the top of the hydrocooler, where it filters through a manifold system and cascades onto the produce before falling into a basic and being recirculated to the chiller for re-use.
The Manifold System
The manfold system consists of three tiers to subdivide the flow repeatedly with a minimum of mechanical complexity. Water first fills a basin into which a set of ten pipes have been embedded. As the water rises it reaches the height of the pipes simultaneously, ensuring that the flow into each pipe is identical. Each pipe then has a series of ten holes drilled along its length, which have been sized so that the greatest difference in flow-rates is below 10%. Finally the flows all exit onto a perforated sheet from which the water falls into the produce.
Diagram of the Electrical System
An electrical control system was devised to monitor the produce temperature and automatically shut the system off at the target temperature. A sharp probe embedded with a thermistor is forced into an item of produce to monitor it's center temperature. When the temperature has been achieved, as determined by an Arduino microcontroller, a series of increasingly powerful relays are triggered to turn off the milk chiller and the pumps.
ANSYS mesh used for analyzing a cucumber
Extensive thermal analysis was carried out, both using the simulation software ANSYS and by hand, to determine the overall heating load various types of produce place on the system and the average cooling time for each type of produce. These estimations were used to compare the hydrocooler to other systems. Cooling times were within 150% of respective literature values, which was determined to be acceptable for a farm with low volume.
Extensive blueprints were created detailing every component of the hydrocooler design and their assembly. Stock components were used wherever possible, and the manufacturing directions and cost estimations of custom components were provided. A detailed bill of materials specifies every component from the supporting angle iron to the hinges used to affix the door.
